A 12-metre section of replacement rail had at least 13 defects that went undetected before the derailment, said George Fowler, a track specialist andTSB investigator, at a news conference in Edmonton on Thursday.

Fractures in the faulty track, installed in 2003, grew until at least one broke, sending the train onto the shores of Lake Wabamun.

The safety board made three recommendations in its latest report:

Set minimum standards for the quality, strength of rails.

Review Canadian rail procedures, equipment used to test tracks.

Establish standards that require thatfatigued rails be replaced.

The report also said weak emergency response plans by both CN Rail and the provincial government contributed to the impact of the spill.

Residents of the village of Wabamun who feel CN did not respond quickly enough to the spill had called for similar recommendations.

An aerial image of Lake Wabamun from August 2005 shows the oil slick that killed 156 birds.

On the second anniversary of the spill in August, health officials warned boaters and swimmers to stay away from oil patches and tar ballsstill in Lake Wabamun.

E. Hunter Harrison, CN Rail's president and CEO, did not respond directly toThursday's recommendations, but praised the "throrough investigation of the unfortunate accident."

In a news release, Harrison said: "I'm pleased to say that CN, as the report notes, has already taken many steps to reduce the risk of recurrence of accidents of this nature, and will continue to do so together with government and industry experts."

In June 2006, Alberta Environment charged CN Rail with failing to take all reasonable measures to remedy and confine a spill, an offence punishable by a maximum penalty of $500,000. The case is not yet resolved.

The TSB said 71 trains have derailed in Canada in the past 10 years because of worn-out rail.